The present invention relates to an apparatus for mounting a plate on a plate cylinder, in which a plate having one end gripped by a leading-side plate lockup device disposed in a gap in the circumferential surface of the plate cylinder is wound around the plate cylinder, and the other end of the plate is gripped by a trailing-side plate lockup device, thereby mounting the plate on the plate cylinder.
A gap having almost a rectangular section and a length almost equal to the overall length of a plate cylinder is formed in the circumferential surface of the plate cylinder for a sheet printing press. A plate lockup apparatus consisting of a leading-side lockup device for gripping and fixing one end of a plate and a trailing-side lockup device for gripping the other end of the plate, gripped by the leading-side lockup device and then wound around the circumferential surface of the plate cylinder, is fixed on the bottom surface of the gap to extend in the axial direction of the plate cylinder. Each of the conventional leading- and trailing-side lockup devices comprises an elongated lockup table extending in the axial direction of the plate cylinder, a plurality of gripper plates, swingably supported at an edge portion of this lockup table by a plurality of bolts, for gripping or releasing the plate with or from the lockup table by being opened or closed as they swing, and a plurality of cams which can be respectively engaged with notches at the edges of the gripper plates. The plurality of cams are aligned along a pivotal cam shaft. A plurality of compression coil springs are interposed between the lockup table and the gripper plates to bias the gripper plates in an open direction.
With the above arrangement, in order to mount a plate on a plate cylinder, when a cam shaft is pivoted, the gripper plates which are divided in the axial direction of the plate cylinder are released upon disengagement from the cams and are simultaneously opened by the elastic forces of the compression coil springs. An end of the plate is inserted between the gripper plates and the corresponding lockup table. When the cam shaft is pivoted in the direction opposite to the direction described above, the gripper plates are pivoted against the elastic forces of the compression coil springs by the behavior of the cams and closed, thereby gripping the end of the plate.
In an apparatus disclosed in Japanese Patent Laid-Open No. 1-127346, a plate lockup table and gripper plates extend in the radial direction of a plate cylinder so that the trailing-side gripper surface of the plate cylinder, which is conventionally formed in the circumferential direction of the plate cylinder, is formed in the radial direction of the plate cylinder. An end of the plate is bent at a right angle by a plate bender which is provided separately. With this arrangement, after a leading end of a plate is gripped and the plate is wound around a circumferential surface of a plate cylinder, the trailing bent portion of the plate is inserted between the plate lockup table and the gripper plates, and the gripper plates are swung by a cam mechanism to grip the bent end of the plate. Thereafter, the overall trailing-side plate lockup device is moved in the circumferential direction, thereby uniformly bringing the plate into tight contact with the circumferential surface of the plate cylinder.
However, in the conventional apparatus for mounting the plate on the plate cylinder, it is difficult to insert the plate in a narrow opening of a leading-side lockup device, leading to a time-consuming operation and much labor. In addition, since the plate which is guided to the trailing-side lockup device while it is wound around the plate cylinder is not brought into tight contact with the circumferential surface of the plate cylinder, it is difficult to insert the trailing end of the plate which is bent almost at the right angle in the opening of the trailing-side plate lockup device, leading to an extra time and an increase in labor. If the plate is not in tight contact with the circumferential surface of the plate cylinder, the plate is deviated during printing to provide unstable printing quality or to degrade the durability of the plate. In order to prevent this, the plate is mounted in the cylinder set state. However, since the printing press must be rotated by one revolution to reach the cylinder set position, the mounting time is prolonged. Also, when the plate is removed in the cylinder set state, an ink remaining on the plate is transferred to the blanket cylinder to soil it.
In order to solve these problems, a plate mounting apparatus as disclosed in Japanese Patent Laid-Open No. 63-19163 is conventionally proposed. FIG. 7 shows this apparatus. This plate mounting apparatus will be described with reference to FIG. 7. A plate cylinder 2 and a blanket cylinder 3 are axially supported between right and left frames 1 of the printing unit to oppose to contact each other. Leading- and trailing-side plate lockup devices 5 and 6 extending in the axial direction of the plate cylinder 2 are disposed in a gap 4 in the circumferential surface of the plate cylinder 2. Plate press cylinders 7 are swingably supported on the frames 1 obliquely below the plate cylinder 2. The operating end of each piston rod 8 of each plate press cylinder 7b is pivotally mounted on a lever 10 supported on the corresponding frame 1 by a pin 9. A roller arm 12 is fixed by split clamping on a pin 11 pivotally supported on a free end portion of each lever 10. A plate press roller 13 is pivotally supported between the right and left roller arms 12.
The operation of the plate mounting apparatus having the arrangement described above will be described with reference additionally to FIGS. 8 and 9. To mount a plate 14, as shown in FIG. 8, gripper plates 5a of the leading-side plate lockup device 5 are opened and closed to grip a leading end 14a of the plate 14. The piston rods 8 of the plate press cylinders 8 are moved forward to swing the levers 10. Then, the plate press roller 13 is moved close to the leading portion of the plate 14 through the roller arms 12. When the plate cylinder 2 is pivoted in the direction indicated by an arrow A in FIG. 8, the plate 14 is wound around the circumferential surface of the plate cylinder 2 as it is urged against the circumferential surface of the plate cylinder 1 by the plate press roller 13. The plate cylinder 1 continues further rotation until a trailing end 14b of the plate 14 which is bent in advance by a plate bender corresponds to the leading portion of the trailing-side plate lockup device 6. When gripper plates 6a of the trailing-side plate lockup device 6 are opened and closed while urging the trailing end 14b by the plate press rollers 13, the trailing end 14b of the plate 14 is gripped by the trailing-side plate lockup device 6. Note that in this prior art, the plate 14 is mounted on the plate cylinder 2 while it is manually held. However, this prior art also discloses a plate mounting apparatus which has a holding unit for holding the plate 14 and causes the leading end of the holding unit to oppose the plate lockup devices 5 and 6, thereby mounting the plate 14 on the plate cylinder 2. This plate mounting apparatus further has an elevating unit, comprising a motor or the like, for vertically moving the overall unit ranging from the plate press cylinders 7 to the plate press roller 13 between an operative position and an retreating position.
In the conventional plate mounting apparatuses described above, however, when each plate press roller 13 is stopped as it opposes the gap 4 in the circumferential surface of the plate cylinder 2, as shown in FIG. 9, since each plate press roller 13 which has been pressing the plate 14 no longer presses it, a portion of the plate 14 near its trailing end floats from the circumferential surface of the plate cylinder 2, as indicated by reference numeral 14c in FIG. 9, and thus the plate 14 is not in tight contact with the circumferential surface of the plate cylinder 2 or is not gripped by the trailing-side plate lockup device 6, leading to an unsatisfactory effect. In order to uniformly press the respective portions of the plate 14 by the plate press rollers 13, components, e.g., the plate press cylinders 7, the levers 10, and the roller arms 12, and the elevating units must be provided on the right and left sides of the apparatus, resulting in an increase in cost. In order to synchronously operate these right- and left-side mechanisms, complicated control is needed. If an elevating unit is provided in the apparatus, since the elevating unit occupies a large area, the work space is decreased, and a blanket mounting operation to a blanket cylinder becomes difficult. Furthermore, since the linear movement of the elevating unit must be converted to the pivotal movement of each plate press roller, control to stabilize the plate pressing pressure becomes difficult. Japanese Utility Model Laid-Open No. 1-76231 discloses a plate mounting apparatus in which a plate is mounted while the trailing end of the plate is held by a metal member of a tensile unit to tighten the plate. However, the metal member of the tensile unit may be caught between the plate cylinder and the blanket cylinder, thus impairing safety.